The Seasonal Cycle

The steady-state, annual average temperature profile is not a very exciting application of a model that is intrinsically able to calculate changes with time. In this section I apply the simulation to a calculation of the seasonal variation of temperature as a function of latitude. The program is listed as DAV09. 

DIM sleq(nrow, ncol), unk(nrow), excoeff(nrow, ncol), ovol(nrow) 

OIM y(nrow), dely(nrow), yp(nrow), incind(nrow) 

OIM land(nlat), oceancl(nlat), landcl(nlat), zatemp(nlat) 

DIM lwflux(nlat), xlat(nlat), albedo(nlat), insol(nlat) 

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Finally, there is the seasonal cycle associated with the difference in climate and weather over the four seasons—winter, spring, summer, and fall (Fig. 4-3). The climatic changes affect source strength, and the weather changes affect transport and diffusion. 

Randerson, J. T., Thompson, M. V., Malmstrdm, C. M., Field, C. B. and Fung, I. Y. (1996). Substrate limitations for heterotrophs Implications for models that estimate the seasonal cycle of atmospheric CO2, Global Biogeochem. Cycles 10,585-602. 

Six, C., Fischer, A. and Walters, S. (1996). The seasonal cycle of atmospheric CO2 A study based on the NCAR Community Climate Model (CCM2), /. Geophys. Res. 101,15079-15097. 

Jouzel, J., Russell, G. L., Koster, R. D. et al. (1987). Simulations of the HDO and H2 0 atmospheric cycles using the NASA GISS general circulation model the seasonal cycle for present-day conditions. /. Geophys. Res. 92(D12), 14739-14760. 

The bias-correction is necessary to correct both the absolute magnitude and the seasonal cycle to that of the observations. This approach assumes that the same model biases persist in the future climate and thus GCMs more accurately simulate relative change than absolute values. It provides a correction of monthly mean climate only and does not correct biases in higher order statistics including the simulation of extreme events and persistence. 

In addition to the diurnal cycle, the seasonal cycle produces much variation in the surface temperature, hence in the processes that control concentration. Concentrations tend to be much higher in the warm summer temperatures when evaporation is driving percolation of the molecules to the surface, than in the winter, when activity may become halted by freezing. Even if no freezing occurs, the processes are slower at colder temperatures, producing lower signature concentrations. 

Derwent, R. G P. G. Simmonds, S. Seuring, and C. Dimmer, Observation and Interpretation of the Seasonal Cycles in the Surface Concentrations of Ozone and Carbon Monoxide at Mace Head, Ireland from 1990 to 1994, Atmos. Environ., 32, 145-157 (1998). 

The seasonal cycle of CCN has also been shown to be correlated with that of cloud optical depth in one remote marine area (Boers et al., 1994), and the isotope composition of non-sea salt sulfate over remote regions of the southern Pacific Ocean has been shown to be consistent with a DMS source (Calhoun et al., 1991). 

Atmospheric column absorption measurements from the surface are possible for NO, N02, NOi3, HNOi3, and C10N02 (23-25). These measurements have defined the seasonal cycle (25) as well as much more rapid variations (26) in the stratospheric levels of N03. Under favorable conditions these measurements can yield information concerning the vertical profiles of the measured species (24, 26). Such techniques can also be used from aircraft platforms (27, 28). 

This chapter discusses the chemical mechanisms influencing the fate of trace elements (arsenic, chromium, and zinc) in a small eutrophic lake with a seasonally anoxic hypolimnion (Lake Greifen). Arsenic and chromium are redox-sensitive trace elements that may be directly involved in redox cycles, whereas zinc is indirectly influenced by the redox conditions. We will illustrate how the seasonal cycles and the variations between oxic and anoxic conditions affect the concentrations and speciation of iron, manganese, arsenic, chromium, and zinc in the water column. The redox processes occurring in the anoxic hypolimnion are discussed in detail. Interactions between major redox species and trace elements are demonstrated. 

Arsenic. The inorganic species arsenate [As(V)] and arsenite [As(III)] were measured in the depth profile of the lake over the seasonal cycle (Figure 6) (32). The relevant reduction and oxidation processes will be briefly considered. The equilibrium constants for the various reactions are calculated on the basis of the thermodynamic data given in refs. 66 and 67. According to the thermodynamic sequence, the reduction of As(V) to As(III) occurs in a p range similar to that of the reduction of Fe(OH)3(s) to Fe(II) (Figure 2). 

Rosenlof, K.H. (1995) The seasonal cycle of the residual mean meridional circulation in the stratosphere, J. Geophys. Res. 100,5173-5191. 

The model clearly captures well the seasonal cycle in temperature at this location. Throughout summer and a large part of autumn, model temperatures are within a few degrees of those observed. In wintertime however, model temperatures at these polar latitudes are somewhat too cold, the dif-... 

Once again it can be seen that the seasonal cycle is well captured and that the wintertime temperatures are somewhat too cold in the model. It is particularly prudent to refine the simulation of these polar wintertime temperatures before chemistry is incorporated into the model, since the temperatures currently lie close to the threshold below which PSCs form and thus could make a substantial difference to the amount of PSCs occurring in the model. 

The summertime N30-50 concentrations of around 100 cm-3 are high, compared to concentrations of around 10 cm 3 in other seasons. At CCN-concentrations, a completely different behavior can be seen, as the, e.g., N100 concentration is during springtime close to 800 cm 3, in comparison with summertime median of 200 cm-3. The day/night cycle at the ZEP station is very strongly connected to the seasonal cycle. 

Smith WO, Marra J, Hiscock MR, Barber RT (2000) The seasonal cycle of phytoplankton biomass and primary productivity in the Ross Sea, Antarctica. Deep-Sea Res Part II 47 3119-3140... 

Smith EM (1998) Coherence of microbial respiration rate and cell-specific bacterial activity in a coastal planktonic community. Aquat Microb Ecol 16 27-35 Smith WO Jr, Nelson DM, DiTullio GR, Leventer AR (1996) Temporal and spatial patterns in the Ross Sea phytoplankton biomass, elemental composition, productivity and growth rates. J Geophys Res 101 18455-18466 Smith WO Jr, Marra J, Hiscock MR, Barber RT (2000) The seasonal cycle of phytoplankton biomass and primary productivity in the Ross sea, Antarctica. Deep-Sea Res II 47 3119-3140... 

To understand the mechanisms governing the seasonal cycles of bioactive elements it is helpful to know the geographic sources of mainstem water as a function of time. Devol et al. (1995) used water discharge data (from the Brazilian Deparatmento Nacional de Aguas e Energia Electrica) to calculate the fractions of water in the... 

Their studies revealed a diverse assemblage of diazotrophs contribute distinct diel patterns that vary over the seasonal cycle depending on the exact composition of the diazotrophic assemblage. 

Anderson, T. R., and Williams, P. J. 1. (1998). ModeUing the seasonal cycle of dissolved organic carbon at Station El in the English Channel. Estuarine Coastal Shelf Sd. 46, 93—109. 

Figure 2 Seasonal and long-term trends in concentrations, and 5 0 values of atmospheric CO2 measured at high latitudes in the northern (Barrow, Alaska) and southern (American Samoa) hemispheres by the NOAA/CMDL-CU flask network (www.cmdl.noaa.gov/ccgg/index.html). The terrestrial biosphere, concentrated in the northern hemisphere, dominants the seasonal cycle. Fossil fuel emission dominates the long-term trends in CO2 and in...

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